Surfactants are used in a variety of applications and processes, but once their task is fulfilled their presence is often undesirable. From an environmental point of view, it is a great advantage if products that ultimately end up in the environment are easily degradable, either biologically or by other means. Also, since surfactants have the ability to form emulsions and dispersions, which in most cases is the very reason for using them, they make the separation of hydrophobic material from the waste water obtained in industrial processes difficult.
In order to improve the degradability of surfactants and make the separation of hydrophobic material from waste water easier, it has been suggested in EP-A1-0 742 177 and EP-A1-0 742 178 to use hydrolysable aldehyde- and ketone-based surfactants. The surfactants, which contain acetal linkages, are stable in alkaline solutions but are hydrolysed in acidic solutions. Acetal-based surfactants are also described in EP-A3-0 054 366.
However, to effect complete hydrolysis the pH need to be lower and the reaction time longer for the acetals as compared to the ortho esters. This will result in a larger consumption of chemicals, and either give a water phase with an unacceptably low pH to be let out to the sewage treatment works or, if the waste water is neutralised, the formation of larger amounts of salt. Furthermore, there is only a small number of long-chain aldehydes that are commercially available, and consequently the range of acetal-based surfactants possible to obtain is limited. In addition the aldehydes are generally more difficult to produce than the corresponding alcohols, and are therefore more expensive.
Ortho ester surfactants have been described in EP-A1 564 402, where an ortho ester group is used for end-capping of nonionic surfactants. The products obtained are low-foaming, and can be used e.g. in machine dish-washing and bottle-cleaning. These products, however, will only marginally benefit from a better degradation, since a hydrolysis step will produce compounds that are still surface active.